Android8.0 Audio系统之AudioPolicy

上一篇我们跟踪分析了AudioFlinger，它是Audio系统的核心，但是AudioFlinger却不能脱离AudioPolicy工作。AudioPolicy模块承载着音频切换，音轨路由的重要工作，没有它，音频输出将乱套。在分析AudioFlinger的时候我们稍微涉及了AudioPolicyService，现在我们重新来看它。在Android7.0中Audio代理部分被组成独立的模块。

void AudioPolicyService::onFirstRef()
{
    {
        ......
        // class AudioPolicyClient : public AudioPolicyClientInterface
        mAudioPolicyClient = new AudioPolicyClient(this);
        mAudioPolicyManager = createAudioPolicyManager(mAudioPolicyClient); //创建Audio管理
    }
}

头文件 AudioPolicyClientInterface 位于 AudioPolicyInterface.h文件中

extern "C" AudioPolicyInterface* createAudioPolicyManager(
        AudioPolicyClientInterface *clientInterface)
{
    return new AudioPolicyManager(clientInterface);
}

extern "C" void destroyAudioPolicyManager(AudioPolicyInterface *interface)
{
    delete interface;
}

对于AudioPolicyClientImpl.cpp实现了 AudioPolicyClient，直接与AudioFlinger交互。对于AudioPolicyIntefaceImpl实现了AudioPolicyInterface直接与AudioPolicyManager交互，

AudioPolicyManager::AudioPolicyManager(AudioPolicyClientInterface *clientInterface)
    :
#ifdef AUDIO_POLICY_TEST
    Thread(false),
#endif //AUDIO_POLICY_TEST
    mLimitRingtoneVolume(false), mLastVoiceVolume(-1.0f),
    mA2dpSuspended(false),
    mAudioPortGeneration(1),
    mBeaconMuteRefCount(0),
    mBeaconPlayingRefCount(0),
    mBeaconMuted(false),
    mTtsOutputAvailable(false),
    mMasterMono(false),
    mMusicEffectOutput(AUDIO_IO_HANDLE_NONE)
{
    mpClientInterface = clientInterface;
    bool speakerDrcEnabled = false;
     //解析 xml Audio策略，路由
#ifdef USE_XML_AUDIO_POLICY_CONF
    mVolumeCurves = new VolumeCurvesCollection();
    AudioPolicyConfig config(mHwModules, mAvailableOutputDevices, mAvailableInputDevices,
                             mDefaultOutputDevice, speakerDrcEnabled,
                             static_cast<VolumeCurvesCollection *>(mVolumeCurves));
    if (deserializeAudioPolicyXmlConfig(config) != NO_ERROR) {
#else
    mVolumeCurves = new StreamDescriptorCollection();
    AudioPolicyConfig config(mHwModules, mAvailableOutputDevices, mAvailableInputDevices,
                             mDefaultOutputDevice, speakerDrcEnabled);
    if ((ConfigParsingUtils::loadConfig(AUDIO_POLICY_VENDOR_CONFIG_FILE, config) != NO_ERROR) &&
            (ConfigParsingUtils::loadConfig(AUDIO_POLICY_CONFIG_FILE, config) != NO_ERROR)) {
#endif
        ALOGE("could not load audio policy configuration file, setting defaults");
        config.setDefault();
    }
    // must be done after reading the policy (since conditionned by Speaker Drc Enabling)
    mVolumeCurves->initializeVolumeCurves(speakerDrcEnabled);

    // Once policy config has been parsed, retrieve an instance of the engine and initialize it
    //代理引擎
    audio_policy::EngineInstance *engineInstance = audio_policy::EngineInstance::getInstance();
    if (!engineInstance) {
        ALOGE("%s:  Could not get an instance of policy engine", __FUNCTION__);
        return;
    }
    // Retrieve the Policy Manager Interface
    mEngine = engineInstance->queryInterface<AudioPolicyManagerInterface>(); //获取引擎
    mEngine->setObserver(this); //设为观察者
    status_t status = mEngine->initCheck(); //初始
    (void) status;
    // mAvailableOutputDevices and mAvailableInputDevices now contain all attached devices
    // open all output streams needed to access attached devices
    audio_devices_t outputDeviceTypes = mAvailableOutputDevices.types();
    audio_devices_t inputDeviceTypes = mAvailableInputDevices.types() & ~AUDIO_DEVICE_BIT_IN;
    for (size_t i = 0; i < mHwModules.size(); i++) {
       //调用ClientInterface加载Audio模块，ClientInterface将调用AudioFlinger的loadHwModule
        mHwModules[i]->mHandle = mpClientInterface->loadHwModule(mHwModules[i]->getName());
        if (mHwModules[i]->mHandle == 0) {
            ALOGW("could not open HW module %s", mHwModules[i]->getName());
            continue;
        }
        //查找输出模块设备
        for (size_t j = 0; j < mHwModules[i]->mOutputProfiles.size(); j++)
        {
            const sp<IOProfile> outProfile = mHwModules[i]->mOutputProfiles[j];

            if (!outProfile->hasSupportedDevices()) {
                ALOGW("Output profile contains no device on module %s", mHwModules[i]->getName());
                continue;
            }
            if ((outProfile->getFlags() & AUDIO_OUTPUT_FLAG_TTS) != 0) {
                mTtsOutputAvailable = true;
            }

            if ((outProfile->getFlags() & AUDIO_OUTPUT_FLAG_DIRECT) != 0) {
                continue;
            }
            audio_devices_t profileType = outProfile->getSupportedDevicesType();
            if ((profileType & mDefaultOutputDevice->type()) != AUDIO_DEVICE_NONE) {
                profileType = mDefaultOutputDevice->type();
            } else {
                profileType = outProfile->getSupportedDeviceForType(outputDeviceTypes);
            }
            if ((profileType & outputDeviceTypes) == 0) {
                continue;
            }
            sp<SwAudioOutputDescriptor> outputDesc = new SwAudioOutputDescriptor(outProfile,
                                                                                 mpClientInterface);
            const DeviceVector &supportedDevices = outProfile->getSupportedDevices();
            const DeviceVector &devicesForType = supportedDevices.getDevicesFromType(profileType);
            String8 address = devicesForType.size() > 0 ? devicesForType.itemAt(0)->mAddress
                    : String8("");

            outputDesc->mDevice = profileType;
            audio_config_t config = AUDIO_CONFIG_INITIALIZER;
            config.sample_rate = outputDesc->mSamplingRate;
            config.channel_mask = outputDesc->mChannelMask;
            config.format = outputDesc->mFormat;
            audio_io_handle_t output = AUDIO_IO_HANDLE_NONE;
            //熟悉的openOutput
            status_t status = mpClientInterface->openOutput(outProfile->getModuleHandle(),
                                                            &output,
                                                            &config,
                                                            &outputDesc->mDevice,
                                                            address,
                                                            &outputDesc->mLatency,
                                                            outputDesc->mFlags);

            if (status != NO_ERROR) {
                ALOGW("Cannot open output stream for device %08x on hw module %s",
                      outputDesc->mDevice,
                      mHwModules[i]->getName());
            } else {
                outputDesc->mSamplingRate = config.sample_rate;
                outputDesc->mChannelMask = config.channel_mask;
                outputDesc->mFormat = config.format;

                for (size_t k = 0; k  < supportedDevices.size(); k++) {
                    ssize_t index = mAvailableOutputDevices.indexOf(supportedDevices[k]);
                    // give a valid ID to an attached device once confirmed it is reachable
                    if (index >= 0 && !mAvailableOutputDevices[index]->isAttached()) {
                        mAvailableOutputDevices[index]->attach(mHwModules[i]);
                    }
                }
                if (mPrimaryOutput == 0 &&
                        outProfile->getFlags() & AUDIO_OUTPUT_FLAG_PRIMARY) {
                    mPrimaryOutput = outputDesc;
                }
                addOutput(output, outputDesc);
                setOutputDevice(outputDesc,
                                outputDesc->mDevice,
                                true,
                                0,
                                NULL,
                                address.string());
            }
        }
        //遍历输入Audio设备
        for (size_t j = 0; j < mHwModules[i]->mInputProfiles.size(); j++)
        {
            const sp<IOProfile> inProfile = mHwModules[i]->mInputProfiles[j];

            if (!inProfile->hasSupportedDevices()) {
                ALOGW("Input profile contains no device on module %s", mHwModules[i]->getName());
                continue;
            }
            // chose first device present in profile's SupportedDevices also part of
            // inputDeviceTypes
            audio_devices_t profileType = inProfile->getSupportedDeviceForType(inputDeviceTypes);

            if ((profileType & inputDeviceTypes) == 0) {
                continue;
            }
            sp<AudioInputDescriptor> inputDesc =
                    new AudioInputDescriptor(inProfile);

            inputDesc->mDevice = profileType;
            ......
            audio_config_t config = AUDIO_CONFIG_INITIALIZER;
            config.sample_rate = inputDesc->mSamplingRate;
            config.channel_mask = inputDesc->mChannelMask;
            config.format = inputDesc->mFormat;
            audio_io_handle_t input = AUDIO_IO_HANDLE_NONE;
            status_t status = mpClientInterface->openInput(inProfile->getModuleHandle(),
                                                           &input,
                                                           &config,
                                                           &inputDesc->mDevice,
                                                           address,
                                                           AUDIO_SOURCE_MIC,
                                                           AUDIO_INPUT_FLAG_NONE);

            if (status == NO_ERROR) {
                const DeviceVector &supportedDevices = inProfile->getSupportedDevices();
                for (size_t k = 0; k  < supportedDevices.size(); k++) {
                    ssize_t index =  mAvailableInputDevices.indexOf(supportedDevices[k]);
                    // give a valid ID to an attached device once confirmed it is reachable
                    if (index >= 0) {
                        sp<DeviceDescriptor> devDesc = mAvailableInputDevices[index];
                        if (!devDesc->isAttached()) {
                            devDesc->attach(mHwModules[i]);
                            devDesc->importAudioPort(inProfile);
                        }
                    }
                }
                mpClientInterface->closeInput(input);
            }
        }
    }
    // make sure all attached devices have been allocated a unique ID
    //遍历输入输出设备，由路由引擎设置各设备的连接状态
    for (size_t i = 0; i  < mAvailableOutputDevices.size();) {
        if (!mAvailableOutputDevices[i]->isAttached()) {
            mAvailableOutputDevices.remove(mAvailableOutputDevices[i]);
            continue;
        }
        // The device is now validated and can be appended to the available devices of the engine
        mEngine->setDeviceConnectionState(mAvailableOutputDevices[i],
                                          AUDIO_POLICY_DEVICE_STATE_AVAILABLE);
        i++;
    }
    for (size_t i = 0; i  < mAvailableInputDevices.size();) {
        if (!mAvailableInputDevices[i]->isAttached()) ;
            mAvailableInputDevices.remove(mAvailableInputDevices[i]);
            continue;
        }
        // The device is now validated and can be appended to the available devices of the engine
        mEngine->setDeviceConnectionState(mAvailableInputDevices[i],
                                          AUDIO_POLICY_DEVICE_STATE_AVAILABLE);
        i++;
    }

    updateDevicesAndOutputs();
}

可以看到AudioPolicyManager通过解析Audio配置文件，加载各输入输出音频Module，然后遍历各输入输出设备，找出稳定的设备后，由路由引擎设置各设备的连接状态。在分析AudioFlinger的时候走过 mpClientInterface->openOutput()函数

sp<AudioFlinger::ThreadBase> AudioFlinger::openOutput_l(.....)
{
    //找到Device, 这个函数很重要，稍后分析
    AudioHwDevice *outHwDev = findSuitableHwDev_l(module, devices);
    //音频流输出到硬件设备
    AudioStreamOut *outputStream = NULL;
    status_t status = outHwDev->openOutputStream(
            &outputStream,
            *output,
            devices,
            flags,
            config,
            address.string());

    mHardwareStatus = AUDIO_HW_IDLE;

在 createTrack_l()的时候，会去根据流类型来获取路由策略

    uint32_t strategy = AudioSystem::getStrategyForStream(streamType);
        for (size_t i = 0; i < mTracks.size(); ++i) {
            sp<Track> t = mTracks[i];
            if (t != 0 && t->isExternalTrack()) {
            //获取路由策略
                uint32_t actual = AudioSystem::getStrategyForStream(t->streamType());
                if (sessionId == t->sessionId() && strategy != actual) {
                    ALOGE("createTrack_l() mismatched strategy; expected %u but found %u",
                            strategy, actual);
                    lStatus = BAD_VALUE;
                    goto Exit;
                }
            }
        }

调用 Audio代理服务的 getStrategyForStream

uint32_t AudioSystem::getStrategyForStream(audio_stream_type_t stream)
{
    const sp<IAudioPolicyService>& aps = AudioSystem::get_audio_policy_service();
    if (aps == 0) return 0;
    return aps->getStrategyForStream(stream);
}

具体的实现在AudioPolicyInterfaceImpl.cpp文件中
frameworksavservicesaudiopolicyserviceAudioPolicyInterfaceImpl.cpp

uint32_t AudioPolicyService::getStrategyForStream(audio_stream_type_t stream)
{
    if (uint32_t(stream) >= AUDIO_STREAM_PUBLIC_CNT) {
        return 0;
    }
    if (mAudioPolicyManager == NULL) {
        return 0;
    }
    return mAudioPolicyManager->getStrategyForStream(stream);
}

uint32_t AudioPolicyManager::getStrategyForStream(audio_stream_type_t stream) {
    return (uint32_t)getStrategy(stream);
}

routing_strategy AudioPolicyManager::getStrategy(audio_stream_type_t stream) const
{
    ALOG_ASSERT(stream != AUDIO_STREAM_PATCH,"getStrategy() called for AUDIO_STREAM_PATCH");
    return mEngine->getStrategyForStream(stream);
}

在文件 frameworksavservicesaudiopolicymanagerdefaultAudioPolicyManager.h 中 AudioPolicyManagerInterface *mEngine; 位于frameworksavservicesaudiopolicyengineinterfaceAudioPolicyManagerInterface.h，在frameworksavservicesaudiopolicyenginedefaultsrcEngine.h文件中被实现如下

  /// Interface members
    class ManagerInterfaceImpl : public AudioPolicyManagerInterface
    {
    public:
        explicit ManagerInterfaceImpl(Engine *policyEngine)
            : mPolicyEngine(policyEngine) {}

        ......
        virtual routing_strategy getStrategyForStream(audio_stream_type_t stream)
        {
            return mPolicyEngine->getStrategyForStream(stream);
        }
        ......
    private:
        Engine *mPolicyEngine;
    } mManagerInterface;

最终将调用Engine.cpp的getStrategyForStream查询音频路由策略

routing_strategy Engine::getStrategyForStream(audio_stream_type_t stream)
{
    // stream to strategy mapping
    switch (stream) {
    case AUDIO_STREAM_VOICE_CALL:
    case AUDIO_STREAM_BLUETOOTH_SCO:
        return STRATEGY_PHONE;
    case AUDIO_STREAM_RING:
    case AUDIO_STREAM_ALARM:
        return STRATEGY_SONIFICATION;
    case AUDIO_STREAM_NOTIFICATION:
        return STRATEGY_SONIFICATION_RESPECTFUL;
    case AUDIO_STREAM_DTMF:
        return STRATEGY_DTMF;
    default:
        ALOGE("unknown stream type %d", stream);
    case AUDIO_STREAM_SYSTEM:
        // NOTE: SYSTEM stream uses MEDIA strategy because muting music and switching outputs
        // while key clicks are played produces a poor result
    case AUDIO_STREAM_MUSIC:
        return STRATEGY_MEDIA;
    case AUDIO_STREAM_ENFORCED_AUDIBLE:
        return STRATEGY_ENFORCED_AUDIBLE;
    case AUDIO_STREAM_TTS:
        return STRATEGY_TRANSMITTED_THROUGH_SPEAKER;
    case AUDIO_STREAM_ACCESSIBILITY:
        return STRATEGY_ACCESSIBILITY;
    case AUDIO_STREAM_REROUTING:
        return STRATEGY_REROUTING;
    }
}

在AudioPolicyService.h文件中定义了如下函数，用来处理设备改变时调整路由策略

virtual status_t handleDeviceConfigChange(audio_devices_t device,
                                              const char *device_address,
                                              const char *device_name);

至此音频代理路由部分暂到这，目前所看到的只是一小部分，随着Android系统的日益复杂，Audio会变得越来越庞大；
不过万变不离其宗，只要大体架构上不做大改动，也是很容易分析的，下一篇我们来看Audio系统的硬件抽象层。

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